The present invention relates generally to plastic optical components and more specifically, to a method and assembly providing a low cost plastic optical lens system that includes a lens, barrel and mount.
Low cost optical components are needed to provide the optical front-end for a variety of devices that have entered the marketplace in the past few years. CMOS image sensors, when compared to charge-coupled-device (CCD) arrays, provide a low cost imaging semiconductor solution for digital cameras, mobile telephones and other optical sensing devices.
In particular, webcams and low cost security systems using similar cameras provide remote observation and security videotaping sources in the workplace and in the home. In some instances cameras are being installed in public places. The demand for low cost cameras has brought about the need for not only a low cost semiconductor imaging solution, but for a low cost optical front end as well.
Typically, the optical front end of a low cost camera includes at least one lens, a cylindrical barrel surrounding and retaining the lens, and a mount for securing the barrel to the camera. The lens is made of a transparent plastic material or glass and the barrel is made of an opaque plastic material so that light can only enter the barrel from an end of the barrel. The mount is usually another plastic part in which the barrel may be inserted.
The optical front end of a low cost camera sometimes includes a mount for attaching the barrel to the camera and an infrared (IR) filter for filtering IR light from entering the semiconductor image sensor. The IR filter is typically adhered to the bottom of the mount and the barrel is fixed to the top of the mount once the module is focused.
During fabrication of the camera, the lens is inserted in the barrel and aligned (typically by forcing the lens against a circumferential ring or step molded or inserted within the barrel). The lens is then secured with an adhesive to hold the lens in place. The assembly of the lens barrel assembly requires a degree of precision commensurate with the optical resolution and other requirements for the camera. As the resolution of the image sensor increases and as the sophistication of camera applications likewise increase, the quality of the optical system must rise to meet the performance requirements of the rest of the camera. In a high-volume low-cost manufacturing environment, maintaining the above-described level of quality is challenging. Also, the adhesive connection may fail when subjected to thermal stress or moisture.
One alternative to the adhesive attached lens-barrel assembly is a one-shot molded lens-barrel assembly. The one-shot assembly is typically a polycarbonate molded piece and is transparent. The barrel of the above-described assembly must then be treated with an opaque paint or inserted within another opaque sleeve in order to prevent light from entering the lens from undesired angles. Treatment of the barrel in the above-described molded part raises the cost of the lens-barrel assembly and also affects durability in that a painted assembly is subject to environmental wear and a lens-barrel-sleeve assembly may separate due to vibration and if glued with an adhesive is subject to the same potential environmental failures as described above for the glued lens-barrel assembly.
Further, as the sophistication of semiconductors cameras increase and as further functions such as focus and zoom are added to high volume applications, multiple lens assemblies are required for the optical front end. Typically these assemblies are manufactured in a manner similar to that described above for a single lens assembly, but with multiple lenses and multiple spacers between the lenses. The multiple lens system and the use of multiple spacers further adds difficulty in holding precision tolerances in a high-volume low cost manufacturing process.
Therefore, it would be desirable to provide a method and system that provide a low cost lens-barrel assembly having precision tolerances. It would further be desirable to provide a low-cost lens-barrel assembly including multiple lenses having precision tolerances. It would also be desirable to mount an assembly, having single or multiple lenses, onto an image sensor assembly (chip on substrate) that does not require focusing.
The above stated objectives are achieved in methods and lens-barrel assemblies molded to form one integral unit. The lens-barrel assembly may be molded to form one contiguous part from a transparent material and an opaque material, or a barrel may be injection molded around an inserted lens, securely retaining the lens. An alternative assembly provides multiple lenses each having an alignment feature for aligning the lens within a molding tool, whereby each of the lenses can be precisely located with respect to each other via mating features for mating with an external mold, and a supporting structure molded at the periphery of the lenses for retaining the lenses in permanent alignment.